Measuring device



March 17, 1942. I GUTTMANN 2,276,302

MEASURING DEVICE Filed Oct. 11, 1939 6 Sheets-Sheet 1 "Howey 5 March 17,1942; E GUTTMANN 2,276,302

MEASURING DEVICE Filed Oct. 11, 1939 6 Sheets-Sheet 2 x mu / [r/c 5.Gaff/Wang. Y

March 17, 1942. GUTTMANN 2,276,302

MEASURING DEVICE Filed Oct. 11, 1959- e Sheefs-Sheet 5 [r/c SGu/fmann.

TTOQEfS March 17, 1942.

E. S. GUTTMANN MEA SURING DEVICE 6 Sheets-Sheet 5 Filed Oct. 11, 1939 NV E. N To Km'c 5. Gaff/Wan MA, CM

(Arrogiays E. S. GUTTMANN March 17, 1942.

MEASURING DEVICE Filed Oct. 11, 1939 Patented Mar. 17, 1942.

UNITED STATES PATENT OFFICE MEASURING nrvrca Eric S. Guttmann, Rockford,Ill., assignor to The Ingersoli Milling Machine Company, Rockford,Ill.,- a corporation oi Illinois Application October 11, 1939, SerialNo. 298,923

' 30 Claims.

The invention relates to a novel measuring device and more particularlyto a device for making precision measurements over comparatively longranges.

Johansson blocks are most commonly employed in making precisemeasurements of substantial lengths, that is, beyond the rangeofordinary dial indicator gauges. These are arranged in an end to endseries to make up approximately the total length to be measured. Amicrometer gauge is placed at the end of the series of blocks to fillout the exact length. For each new length to be measured, another.appropriate series of blocks must be selected and set up. Not only isthis method cumbersome and slow, but, in addition, a large amount ofmental calculation is entailed in adding up the separate components.Possibilities of error are great not only because of the computationsinvolved but also because any grease or foreign matter sticking to theabutting 'block ends will result in a serious error.

The general aim of the present invention is to overcome the foregoingobjections by providing a precision measuring instrument which aflordsan instantaneous and continuous indication of the displacement of amovable member with a high degree of accuracy, iorexample, a thousandthof an inch or less in the case of linear measurements. Accordingly, ameasuring device embodying the present invention may be associated witha movable machine tool element and the operator need merely read thedial of .the instrument to obtain at any time an accurate measure ofdisplacement throughout a long range.

A more detailed object is to provide a measuring device involving arotatable drum and a flex-' ible element or line wound helicallyth'erearound with the drum and the unreeled portion of the elementmounted and guided for relative movement in a manner such as to maintaina con stant angular relation between the drum axis of the flexibleeleurements from a given reference point.

In a'measuring device of the above character,

' the indicator is constructed for use with a drum precisely of givensize and with aline of certain thickness. Any deviation from these exactdimensions will introduce an error in the indication and this error willaccumulate throughout the operating range of the device.

. still another object of the invention is to correct for such errorsand thus adapt the device for precise indication in spite of dimensionalinaccuracies in the size of the drum and line.

A more detailed object is to provide for progressively changing thelength of line paid out or reeled in per unit of the measured movement,the amount of suchchange corresponding in magnitude to the error due tosaid dimensional inaccuracies.

The invention also resides in thenovel manner in which the compensatingcorrection is introduced.

Another object is to provide a measuring device of the characterembodying a novel arrangement including an electric motor for performingthe dual functions of winding up the tape and eliminating backlash inthe gears.

The invention also resides in the novel constructions which minimize thechanges required to adapt the measuring instrument to widely varyingranges and which avoid the introduction of errors by the accumulation offoreign matter on the tape or drum. I

Still another object is the provision of a unit embodying a novel formof take-up drum by means of which errors may be obviated which wouldotherwise result from changes in tape angle, tape tension, or both.

It is also an object to provide a novel drum construction by virtue ofwhich extreme precision of dimensioning is combined with low cost ofproduction.

Further objects and advantages of the invention will become apparent asth following description proceeds taken in connection with theaccompanying drawings, in which Figure'l illustrates diagrammatically ameasuring device embodying the present invention.

Fig. 2 illustrates diagrammatically the operation of an adjustmentmechanism included in the device in Fig. 1.

Fig. 3 is a front elevation partly in section of a millingmachine' headillustrating one adaptation of the invention.

Fig. 4 is a detail transverse sectional view along the line d& in Fi 3.

Fig. 5 is a vertical sectional view along the line 5-5 in Fig. 3.

Fig. 6 is a face view of the visual indicator.

Fig. 7 is a side elevation partly in section oi the drum and tape unit.

Fig.'8 is an exploded perspective view of the drum. 1

Fig. 9 is a fragmentary longitudinal sectional view of the drum.

Fig. 10 is a longitudinal sectional view along I the line iii-4B in Fi6.

Fig. 11 is a transverse sectional view along the line Hll in Fig. 10.

Fig. 12 is a transverse sectional view along the line 12-32 in Fig. 11.

Fig. 13 illustrates diagrammatically the application to a machine toolhead of a modified form of the measuring device.

Fig. 1. is an enlarged side elevation of the drum and tape unit includedin the device of Fig. 13.

Fig. 15 is an explanatory diagram for the device of Fig. 13.

Fig. 16 is a fragmentary perspective view illustrating the applicationof the measuring device to a machine tool work table.

Fig. 17 is an enlarged transverse sectional view along the line iii-I9in Fig. 15.

While the invention is susceptible of various modifications andalternative constructions, I have shown in the drawings and will hereindescribe in detail the preferred embodiment, but it is to be understoodthat I do not thereby intend to limit the invention to the specificforms disclosed, but intend to cover all modifications and alternativeconstructions falling within the spirit and scope of the invention asexpressed in the appended claims.

Since the measuring device herein disclosed is essentially a precisioninstrument, it is especially useful in connection with machine tools inview of the high accuracy of measurement demanded in their operation.Accordingly, the invention has been shown herein as applied to variousforms of machine tools but it will be appreciated that measuring devicesembodying the present invention are also susceptible of a wide varietyof other applications.

General arrangement 0! facts In the illustrated embodimentythe devicecon-- stituting the present invention gives a continuous reading on avisual rotary indicator ID (see Fig. 1) of the linear displacement, froma reference point P, of some movable member ll along a predeterminedpath AA. For this purpose, motion of the member II is transmitted to theindicator through an elongated element or line having one end attachedto said member and connected to a rotary part which is geared in theproper ratios to the different parts of the indicator. element comprisesa flexible tape in the form of a very thin fiat metal strip or ribbon I!having its free end I3 fixed to the member H, and the rotary partcomprises a freely rotatable drum H around which the remainder of thetape is helically wound with its end anchored to the drum at l5. Asshown, the drum axis is disposed substantially perpendicular to therectilinear path in which the movable member I I is guided and thispath, for a reason to appear later, is disposed at one end of the tapehelix. The'drum H is rotat- Preferably, though not necessarily, the.

member ii and various parts of the indicator,

the rotor of the torque motor It being fast on the shaft 24 so that themotor also serves to take up any backlash in the gears l8 and 20.

The ratios of the sets of gears i8 and 20 are so chosen, and the scaleof the indicator I0 correspondingly calibrated, that the indicator willread directly in terms of linear displacement for the movable member ii.For purposes to appear later, the indicator is divided into two parts,one preferably being a wheel type counter for indl cating primary unitssuch as inches and also tenths of such units, the other being a dialtype counter for indicating secondaryunits such as thousandths (see Fi6).

To simplify the calculations for thegear ratios in the instrument andits calibration, it is desirable that the arrangement for driving thedrum id be such that a point on its peripherywill move through adistance exactly equal to that moved by the member I I. This is to becontrasted with an arrangement in which instead of these distances beingequal they'are merely proportional, even though they bear a fixed ratio.To use a specific example, if the circumference of the drum i4 is teninches, then the arrangement should be such that, in spite of the factthat the tape extends helically aroundthe drum, the latter will makeexactly one revolution while the member H is moving a distance of teninches from point P to point P1. To accomplish such motion of the drumand at the same time compensate for travel of the point of tape lead offalong the drum, a particular relation of the drum, tape and path of themovable member is'maintained. In particular, the'arrangement preferablyis such that the tape I2 is hellcally wound on the drum and eachsuccessive convolution is led off at exactly the helix angle. That is tosay, the drum, in addition to being positioned with its axis I!generally perpendicular to the path A-A in which the movable end I3 isguided, is positioned axially with the end of the tape helix, when fullywound up, disposed adjacent but spaced inwardly from the path A--A by anamount such that the unreeled portion of the tape is disposed at aconstant included angle a to said path. Although this spacing of thepoint of tape lead-oil from the drum increases progressively as the tapeis unwound, the angle a, due to the guiding of the free end of the tape,will remain-fixed for all of the positions of the tape some of which areindicated by dotdash lines in Fig. 1, the angle being equal to the helixangle of the tap wound on the drum. When so arranged the actual lengthof tape unwound from the drum, while the member II is moving betweenpoints P and P1, will be VIOH-pitch", the "pitch" being, of course, thedistance between'adjacent convolutions 'of the tape.

It will be observed that the angle between the drum axis l1 and theunreeled length of tape between the point l3 and the point of lead-oilfrom the drum also remains constant for all positions of the movablemember H- and deviates requiring different ranges.

2,970,362 froma right angle by an angle equal to the helix angle of thewound tape.

'I'he:foregoing calcaulations hold'true only in the case of a tape ofinfinitesimal thickness. Actually the point, which moves about the druma distance equal to the linear displacement of member H, lies not on thedrum periphery but on an imaginary circle concentric with the drum beadapted, with a minimum of change in the.

parts of the instrument itself, for installations In particular, if thegearing I8 is arranged so that the take-off shaft 2| will have somestandard angular rotation for each unit of linear displacement of themovable member H (e. g. one revolution of shaft 2| for each inch ofdisplacement of member ll), then all of the parts lying to the right ofthe gearing I8 in Fig. 1 may be of identical form for all instrumentsregardless of their ranges. The range requirements of a particularinstallation may be obtained by varying the length of tape and tapewinding capacity of the drum It by changing either the length ordiameter of the drum; Having chosen a drum diameter suitable for aparticular installation, the gearing I8 is then calculated to afford,the desired standard ratio noted between angular displacement of itsout- .put shaft 2| and linear displacement of the member H.

Application to tool spindle ter 23 is carried by a spindle 26 journaledwithin a quill 25, which is splined against rotation and accuratelyguidedwithin the tool head or housing 26 for axial adjustment in arectilinear path. The guideway for the quill is indicated at 26 (Figs. 4and 5). The quill 25 is shifted axially, by power or by hand, byrotating a pinion 21 meshing with a rack 28 on the side of the quill.The tool head 25 is traversed horizontally along a rail 29 by lead screw30, and a suitable driving motor 3! is provided in the head for thespindle 25.

For this application, the measuring device includes the drum I4 with itstape l2 helically wound as previously described. In the presentinstance, the drum shaft I1 is journaled in suitable anti-frictionbearings within a sleeve 32 located within the head 26. This sleeve isadjustable about a horizontal axis on a pivot 33 (Fig. 4) to swing thedrum It about this axis,

for a purpose which will hereinafter appear;

The adjustment is accomplished by a pair of opposed screws as, threadedin brackets 35 in the tool head, and bearing against opposite sides ofthe sleeve. A removable cover plate 35 on the tool head gives access tothese screws.

The visual indicator I0 is located within a 7 suitable housing 38 (Fig.3) fixed on the end of the sleeve 32. The indicator face is thus exposedat the side of the machine tool head 26 and can times.

In the present instance, to a block or' bracket 31 (Fig. 5) screwed onthe side of the quill 25', and the cylindrical portion of the guideway26 in which the quill is slidable is slotted longitudinally as indicatedat 38 to receive the tape.- Thus, the guideway 26 causes relativemovement between the drum and the free end I301 the tape in a planewhich, except for the compensating adjustment later to be described, isnormal to the drum axis. A sheet metal housing 39 covers this slot aswell as the drum It so that the drum and tape are completely enclosed toexclude any dust or dirt. It will be appreciated that precision ofoperation requires hat no dirt shall become lodged between the tape anddrum since even any small particles would bulge out the tape and destroythe accuracy of the instrument. As a further precaution, pads 40 of feltor the like (Fig. 5) are arranged to contact the faces of the tapeadjacent the drum so as to wipe or scrape off any foreign matter whichmay come onto the tape while it is unwound.

It should be particularly noted that the'tape I2 is attached tosubstantially the central portion of the quill 25 and also that the drumand tape are located on the interior of the tool head. Such anarrangement of the parts not only promotes compactness but in additioninsures a substantial uniformity of temperature throughout the tape anddrum unit as well as the machine tool parts including particularly thequill 25. In the event that the tape and drum are made of materialhaving substantially the same coeiiicient of thermal expansion asthe'quill, any change in length of one, due to a change in temperature,will in such case be automatically compensated by a corresponding changein dimension of the other.

With the arrangement shown, the tape I2 is reeled inand'out on the drumIt as the quill 25 is moved down or up. The indicator I0 is thusactuated, in a manner heretofore described, to give a continuousvisualreading of the exact location of the-cutter 23. v

Drum and tape unit Accuracy of measurement is, in the presentinstrument, dependent directly upon .the precision with which theeffective diameter of the drum actually conforms to a selected value. Ifthis effective diameter is inaccurate by only, say a 0.0001 of aninch,there will be an inaccuracy of several thousandths of an inch in thetotal registrations of the instrument since each convolution of the tapeabout the drum multiplies the error. To meet this diiiiculty, a novelform of drum and tape unit has been provided by means of which theextreme precision in dimensioning can be accomplished at comparativelylow cost.

In the instant embodiment (Fig. 7 the drum it is fashioned in the formof a cylindrical sleeve with suitable interior'webs 6| by which it isfixed to its shaft IT. The drum is preferably made of metal having-avery low coefiicient of thermal expansion such, for example, as Invar.Since the surface of the drum is of simple cylindrical form, it can beground with extreme precision by simple and inexpensive grindingprocess. To form a guideway for the tape i2, a helical groove at (Fig.8) is cut in the drum surface and a separately formed guide element comprising a helical spring 63 of square cross section .be viewedconveniently by the operator at all.

the tape I2 is fixed. 5

is located in this groove. The .spring can be expanded and slipped intoplace on the drum after the surface of the latter has been groundaccurately to the desired diameter. The resilient engagement of thespring with the drum grooves locks it in place. It has been found thatthe clearance between the side edges of the tape 12 and the abuttingwalls of the spring 43 can be fairly large without impairing theaccuracy of the instrument (Fig. 9). In fact,ia clearance of 0.008 of aninch has been found suitable for.

the purpose so that the construction is satisfactory, even though thecross section of the spring 43 is not dimensioned with extreme accuracy.

With the coil spring 43 assembled on the drum M (Fig. 7) as describedabove, it will be seen that a helical groove is defined to receive thetape l2. The net result is to provide what amounts to a threaded drumwith the roots of the threads ground to diameter with extreme precision.Since this grinding is, however, carried out on a simple cylindricalsurface, rather than as a part of a thread-grinding operation, the costis' comparatively low.

As was previously noted, the thickness of the tape as well as the actualdrum diameter must be taken into account in calculating the eflectivediameter of the drum, shown as diameter D in Fig. 7. This being thecase, careful attention must also be given to tape thickness- The tape I2 is preferably made of flexible spring steel both because of itsflexibility and its resistance to elongation under tension. Accuratelysized steel tape suitable for the present purpose is commonly availableon the market.

and 4). The axis of pivotal adjustment lies at 1 right angles to thedrum axis and to the path A-A for the end of the tape (Fig. 1).

over, the pivotal axis is coincident with a radius of the drum passingthrough the center line of the tape at the latter's point of tangency tothe drum for the first convolution of tape. With the drum pivotallymounted in the manner described, it can be swung toward or away from theportion of unreeled tape (Fig. 2). This bodily adjustmentof the drum is,of course, accomplished by the screws 34 bearing against the sleeve 33.

A thin flat tape is preferably utilized rather maximum flexibility withmaximum strength.

A strip of rectangular cross section as shown has a minimum moment ofinertia, as compared to a round cross section and, hence, greatestflexibility.

Compensating adjustment- Despite all precautions which may reasonably betaken in dimensioning the parts of the drum and tape unit as heretoforenoted, there" are likelyto be some unavoidable variations in diameterfrom end to end of the drum and also variations in tape thickness fromend to end of a particular piece of tape. These give rise to acumulative error in registration over the range of an instrument.

Provision is made for distributing this otherwise cumulative errorthroughout the range of the instrument so that the error will benegligibly small at any particular point. Generally, this isaccomplished by inclining the drum axis away from a perpendicular to thepath of travel of the movable member II in a direction and by an amountcorresponding to the,compensation to be efiected. It is for this purposethat the drum I4 is mounted to pivot at- 33 (Figs. 3

In setting up the apparatus the tape is first reeled in and theindicator 10 set at its zero position. Then, the tape is reeled out toits full extent and the distance which its free end has moved ismeasured accurately in any suitable way such as the Johansson blockmethod. This independently measured distance is then compared to thereading of the indicator I0 to see if the latter is correct. If there issome variation in'diameter of the drum from end to end or variation intape thickness, there may bean error in the indicator registration of afew thou- .sandths of an inch. If such is the case, the drum i4 istilted about its pivot 33 until the indicatorl0 registers exactly thecorrect distance as meas ured by the Johannson block method.Incidentally, if the indicator reading is high when the tape has beenunreeled to'any desired point preferably the outermost limit of therange through which measurements are to be made with the drum axisdisposed perpendicular to the path AA of movement of the member II, theaxis would be tilted toward the free end of the tape, that is,downwardly as represented onan exaggerated scale by the lower dot-dashposition in Fig. 2. The amount of such tilting is, of course, very smalland the distance that the tape lead-off point is shifted along the drumaxis is even smaller; consequently, the change in the tape angle a abovereferred to is negligible. The angle therefore remains, for allpractical purposes, constantand equal to the helix angle of the woundtape. Conversely, if the indicator reading, when the tape is unwound, islow, the angle between the drum axis l1 and the path AA will beincreased a proper amount beyond a right angle as represented by theupper dot-dash position in Fig. 2. I

After having made the adjustment described above, the indicator in, ofcourse, registers properly when the tape is fully extended. It alsoregisters properly when the tape is fully wound up; that is, in the zeroposition. In other words, the precision of the instrument is absolute atboth ends of its range of registration so that the error heretoforenoted is now distributed throughout theintermediate registrations of theinstrument. In this way the error, which is at most only a fewthousandths of an inch, is so divided that its effect at any particularpoint is negligible.

It will be seen from the foregoing that the result of tilting the drumaxis away from a perpendicular to the path of travel of the movableelement is to change the effective ratio of-motion transmission betweenthe movable element and the indicator which connection, in the presentdisclosure, includes the tape l2, the drum I 4, and the drive gearingbetween the drum and the indicator Ill. The sense and the amount of thechange in the motion transmitting ratio corresponds to the rate of erroraccumulation Moresively throughout the range of the movement to bemeasured.

It will be observed that during the compen sating adjustment abovedescribed, the main movement of the point of lead-off of the tape fromthe drum is transversely of the drum axis. Because this point moves inan are about the pivot 33, the position of the lead-oif point shifts toa much smaller degree longitudinally of the drum. For errors of thesmall magnitude ordinarily involved, this shift is so extremely smallthat it does not change the angle a to a measurable degree. Accordingly,the angle a remains constant for all practical purposes in all positionsof the movable support after the compensating correction has beenintroduced.

Tape tensioning mechanism with changes in displacement of the end of thetape."

The torque motor It may be an ordinary shaded pole induction motorenergized from any suitable source of single phase alternating currentand its supply circuitsarepreferably interlocked with those of themachine tool to which I it is suflicient to note that the wheel 45rotates continuously, the. wheel 45 makes one-tenth of a revolution foreach full revolution of the wheel the instrument is applied so that thetorque motor It will be excited automatically whenever the machine toolis in use. The motor l6 may be conveniently mounted by a bracket 4%(Fig. 10) within the indicator housing 36 and as was heretofore noted,its rotor 22 is fixed to the The left end (as viewed in Fig. 10) of theshaft 2| is connected to the drum shaft I? through the gearing l8 which,in the present instance, consists of a gear l8 fast on the shaft I! anda pinion l8 fast on the shaft 2|. At its opposite end the shaft 2| isconnected to a central shaft 50 for the indicator through the gearing20, which includes a gear 20 fast on the shaft 2| and a meshing pinion20 fast on the shaft 50 In addition to exerting a constant andcontinuous tension on the tape it, the motor 16' also serves to take upany backlash in the gearing l8, which backlash would otherwise seriouslyaffect the accuracy of the final indication owing to the fact that thedrum movement is magnified many times while being transmitted to theindicator. Any backlash in the other gearing does not introduce errorsof objectionable magnitude.

Indicating mechanism a mark 52 on the dial plate.

, and similarly the wheel 45 advances onetenth of a revolution for eachfull' revolution of the wheel 45.

through registering apertures 45 in a dial 'plate 47. 'This dial plateis in turn covered by a glass bezel 48 on the front of the casing 36(Fig. 1),

the counter mechanism 45 being carried on a bracket 35mounted on thep'late 36.

The reading in tenths of the primary units is much too coarse'for use inprecision work as,

comprises herein a supplemental open face dial type of revolutioncounter indicator which has been provided for showing displacement inincrements of hundredths and thousandths ofv an inch. As shown in Fig."6, this dial type indicator includes a circular graduated scale tQjonthe dialplate 47, and a continuously revoluble pointer or needle 50.Each increment on the scale 49 represents one-thousandth of an inch sothat the pointer 50 makes one complete revolution for each tenth of arevolution for the counter wheel 45 and for one-tenth of an inch oftravel of the movable machine element or a point on the imaginary drumcircle above referred to.

The pointer 50 is quite lightand easy to revolve, and in addition it isnot connected directly to a counter wheel or the like, which it mustactuate step -by-step during each revolution, so that even though themovable member I! may be moved at a speed as high as forty feet perminute, there is no danger of injury to the instrument despite thesmallincrements which it is adapted to register.

To correlatethe readings on the counter wheel 45 with those of thepointer 50, a series of transverse lines 5| (Fig. 6) are placed on theperiphery of the wheel extending through the center of each of thecorresponding digits marked on it. These lines are adapted to registerwith The operator is thus aware that the thousandths indicated by thepointer 5i) must be added to the exposed digit on the wheel 45 lyingabove the line 5| un- 45 is connected to the shaft 2! without theinterposition of any speed change mechanism since, as was heretoforenoted, this shaft is arranged, by proper selection of gearing it, tomake one revolution for each inch of tape unreeled from the drum iii, Inthe present embodiment (Figs. 10, 11 and 12), a bevel gear 53 fast onthe wheel 35 meshes with a bevel 1 gear 54 loosely journaled on theshaft 25. This latter gear is fashioned on the hub of the gear 20 andwhich also constitutes the driven member of the clutch l8. A compressionspring 56 urges this driven member 20 into face-to-face Digits fromzero' to nine are marked on the peripheries of each ofthe'se-wheels inthe usual manner and they are exposed toiviewur' driving member 51 faston the shaft 2!. So long as the clutch l9 remains engaged, the counterwheel 45 is thus driven in synchronism with the shaft 2|. Thestep-by-step advancing motion of the other two counter wheels 45'' and45 is imparted to them from wheel 45 in, the usual manner for suchdevices.

A separate driving mechanism for the pointer 50 is provided between itand the shaft 2!. In

' the present instance, the pointer is fast on the end of the shaft 50"(Fig. 10) This latter shaft is driven through the gearing 20 at a speedten times that of the shaft 2| so that the pointer 50 will make onecomplete revolution for each tenth of an inch of tape unreeled from thedrum H.

Resetting of indicator Occasion very frequently arises for changingthe-reference point from which measurements are to be made in using aninstrument of the type described. For example. when applied to a machinetool as in Fig. 3, measurements may be made from several differentreference cuts. Provision is made for setting at least the fineincrement indicator to zero so that the subsequent measurements can bemade by direct readings from the instrument rather than by making amental calculation each time tosubtractthe reference cut reading fromthat of the indicator.

It is-to accommodate such a resetting operation that the clutch l9(Figs. land 11) is interfrictional engagement with a cup-shaped clutchleased, the clutch parts being then engaged with the pointer in itsreset position.

- position by slipping of the clutch is. The dial posed between theindicator l0 and the drum l4.

This clutch must, however, be of a type in which its driving and drivenmembers can engage in any relative angular position whatsoever, africurged into gripping engagement at their adjacent surfaces by acompression spring 58 which encircles the shaft 2| and acts between themember 2i] and a stop on the end of the shaft. The clutch also servesas'an overload release which prevents the tape II from being stretchedor broken if an operator inadvertently changes the indicator settingwithout previous disengagement of the clutch.

During the resetting operation, it is desirable that the shaft 2i beheld against rotation so that the tape tension will not be changed andan error introduced as an incident to such resetting. For this purpose abraking plunger 58 (Fig. 11) is arranged for frictional engagement withthe periphery of the driving member 51 of the clutch. A compressionspring 59 normally urges the plunger out of engagement with theclutchmember 51, this plunger being arranged for axial sliding movement withina block 80 screwed on the supporting plate 36. The head of the plungerextends outside the casing in the form of a convenient push button 58 sothat the plunger may be pushed in axially to bring the brake shoe 58into engagement with the clutch member 51, thus holding it firmlyagainst rotation. I

. To reset the dial pointer 50, the operator pushes in the plunger 58 tohold the clutch driving member 51 against rotation. Then, he grasps aknurled head 60' (Figs. 10 and 11) fast on the end of the shaft 50 andturns the pointer 50 to the desired position, usually zero, the clutchl9 slipping to permit such movement. The wheel counter of course, isturned slightly during this adjustment. Finally, the brake is repointeralso turns during such resetting. .A spring 82 encircling the shaft 62urges it outward to thenormal disengaged position for the gear 63.

Brief resum of operation.

When the measuring apparatus is installed in a machine like that of Fig.3, it is first of all adjusted as by the adjustment screws 34 in orderto distribute throughout the range of the instrument any errors arisingfrom variations in diameter of the drum from end-to-end, or variationsin tape thickness. The drum and tape unit is, of course, fashioned inthe manner heretofore described so as to obtain maximum accuracy in itsdimensions prior to its installation in the machine.

In the operation of the machine, the operator ordinarily starts in on anew work piece by taking a reference cut. usually for roughing. He

then resets the indicator III to zero, as described,

- cutter 23 (Fig. 3) at successive positions of axial displacementrequired, hesimply traverses the quill 25 until the indicator l0 (Fig.6) shows that the desired position has been reached. The readingafforded by the instrument is continuous and precise throughout longranges so that through the use of ordinary jogging controls the cuttercan 'be brought precisely to the desired position.

As-the quill 25 is traversed, the tape I2 is wound in or out on thetake-up drum i4, depending upon the direction of quill movement, thedrum being yieldably biased at all times by the torque motor IE to reelin the tape. Since the drum is constantly connected to the indicatorill. the reading of the latter gives a continuous indication of amachine tool elements position.

The operator can, of course, reset the indicator ill to zero, or to anyother desired position when-- ever required. In this connection, it issometimes easier to predetermine the measurement before movement of themachine element. To do this, the instrument is first set manually toindicate the exact distance desired to be measured and then the machineelement is shifted in a direction to reel in the tape l2. The arrival ofthe element at the exact position required will be indicated by a zeroreading on the instrument.

Application to parts difficult of access' as was the case of themounting for the'quill 25 in Fig. 3. In such case the tape I2 is ledover idlers 69 and down to a winding drum located at the side of thehead 68 where ample space is available. w

Although the use of idlers as described above to direct the .tape I2into comparatively inaccessible machine parts adds greatly to theversatility of use of the measuring device, it introduces otherdifliculties with-respect to precision of operation. In the installationof Fig. 13, for example, the tape I2 is helically wound about a drumconnected to an indicator III as before. In this case, however, it willbe seen as the tape is unwound from the drum, the length of tape lyingbetween the idlers 69 and the drum gradually increases. In other words,as the end of the tape moves from position, P2 (Fig. to P3, through adistance .r, the portion of tape between the drum and the idler 69increases in length-from 11 to z.

This would, of course, introduce a serious error in the readings of theindicator III.

To eliminate the error in measurement .which would otherwise result fromthe action described above, a drum I4 (Fig. 14) of special contour isutilized. This drum may be made from Invar as sealed against the beforeand the helical channel for receiving the tape defined by a spring 43(Fig. 14) The drum is, however, formed with a curved taper from end toend, the change in contour being calculated so that the portion of thetape lying between the drum and the idler will remain constant assuccessive convolutions of the tape are unwound. It will be noted toothat there is some change in angular relation of the tape to the drum asit is unwound, so that it does not exactly match with the helix angle ofthe tape-receiving groove on the drum periphery. This angular relationhas been shown in exaggerated form in Fig. 14. By providing asubstantial clearance of, say, 0.008 of an inch between the edges of thetape and the sides of the spring 43 this change in angular position oftape is permitted without interference with its proper winding and unwinding.

The adaptation of the invention as shown in Figs. 16 and 17 forms thesubject matter of my copending application Serial No. 401,940, filedJuly 11, 1941.

Tape protection depending from and fixed to the underside of the table,preferably near the longitudinal center thereof.

v To protect the tape, an elongated plate ll of a width corresponding tothe-travel of the tape.

along the drum throughout the range of table movement, is bolted to thebed so as to overlie the tape. The space between the free edge of theplate and the bed surface I3 is sealed by a strip I2 of yieldablematerial, such as rubber, seated in a channel II attached to the plate.

As the table moves lengthwiseof the tape enclosure, the arm Ilridesalong beneath the free edge of the strip I2. Due to its resiliency. thestrip I2 presses down firmly against the wall I3 except at the pointwhereit is locally displaced by the arm, and accordingly the chamber II,in which the tape I2 is housed, is eflectually entrance of dirt or otherforeign material which might lodge on thetape. This kind of protectionmay be provided for the tape when the measuring device is applied to anyother movable machine element.

From the foregoing it will be apparent that the improved measuringdevice possesses numerous outstanding advantages. By virtue of thecontinuous engagement of the driving connection between the drums andindicators, the device measures all movements of the movable member withfull accuracy. and this in spite of high traverse speeds that arefrequently used. Because of the continuous indication, coupled with theprovision for manual reset, no complicated manipulations or calculationsare involved in making a measurement and labor costs are'accordinglyreduced. For example, time studies made in actual service use of amilling machine show that the same skilled operator using the improvedmeasurlngdevice is able to make a setup for a finishing milling cut inone-sixth the time that is required using Johansson blocks of the kindcommonly used in machine shops, substantially the same accuracy beingobtained in both cases.

There is no possibility of error being intro- Figs. 16 and 1'?illustrate the manner of apply- 1 which the table slides in ways which,in this instance, constitute the means for guiding the free end of thetape and thus maintain the proper constant angular relationship betweenthe drum axis and the unreeled portion of the tape I 2. The tape I2 isled along a wide channel between the bedways with its end attached to anarm 19 disposed close to the upper bed surface I3 and projectinghorizontally from a bracket I5 The present measuring device involves theconversion of the movements of the machine element into rotary motion ofthe indicator parts and thus is readily adaptable to remote indication.This may be accomplished, for example, by driving a so-called Selsyntype transmitting motor from the shaft 21 and utilizing an associatedSelsyn type receiving motor operating through a normally engagedmanually disengageable friction clutch to drive the pointer 50 of aremotely located indicating instrument directly and to drive appropriatespeed reduction gearing for actuating the wheel counters.

Finally, the instrument, with the extreme accuracy required in theoperation of machine tools, may be manufactured at a low cost which isnot increased in proportion to changes in the I range of the instrument.

a structurally separate helical member encircling said drum and fixedthereon to define between its convolutions a helical .channel. with anaccurately formed root on the drum periph-.

ery, a thin flexible element wound about said ranged and very thinfiexible sheet we, a drive shaft for said mechanism,

drum in said channel with one end fixed to the drum and the otherarranged to be unreeled therefrom, an indicator, and means driven bysaid drum for actuating said indicator inresponse to drum rotation.

ical channel with an accurately formed root on the drum periphery.

3. In a precision measuring instrument of the type described, thecombination of a drum and tape unit comprising a rotatable drumpresenting a peripheral helical groove having a fiat and -,accuratelyformed root surface, a tape helically wound about said drum in saidgroove with one end anchored to the drum and the other arto.be pulledfrom it to rotate the drum, said tape being fashioned from a strip offiat closely to said root surface when wound about the drum while beingsubject to minimum elon-.

gation when placed under tension.

4. In a precision instrument for measuring the displacement of a movablemember, the combination of a revolution counter type of indicatingmechanism calibrated in terms of linear measure and including a shaft, arotatable drum of accurately formed exterior diameterTaTgear connectioninterposed between said shaft and drum, the ratio of said gearconnection being such as .to revolve said shalt through precisely onerevolution in response-to the displacement through a selected unit oflinear measure of a point lying on a circle concentric with said drumand of predetermined diameter, and a thin flexible tape helically woundabout the drum with one end anchored to the drum and the other to amovable memb r whose displacement is to be measured, the thickness ofsaid tape being precisely the difference between the actual peripheraldrum diameter and said predetermined drum diameter.

5. In a measuring device, the combination ofan indicator mechanism ofthe revolution counter type calibrated in terms of linear measarotatable drum, a flexible line helically wound about the drum andanchored at one end to the same with the other end of the line arrangedto be at- 'tached to a member whose displacement is to be measured, andmeans including a replaceable gearing interposed between said shaft andsaid drum for rotating said shaft precisely one revolution for eachdisplacement of said other end of said line through a unit of linearmeasure, whereby said mechanism may be conditioned through choice of asuitable ratio of said replaceable gearing for attachment to drums ofdifferent diameters.

6. A measuring device comprising, in combination, a revoluble take-upreel havinga flexible line wound about it and anchored at one end to thereel with the other end free to be unreeled maintain a constant tensionin said line but also metal to conform I aavasoa to take up backlashplay in said gear connection.

7. A device of the type described comprising, in combination, arevoluble take-up reel having a flexible line wound about it andanchored at one end to the reel with theother end free to be unreeledfrom the reel and adapted for attachment to a movable member, indicatormeans actuatable in response to reel rotation, gearing for transmittingthe motion of said reel to said indicator means at increased speed, andan elec-- tric motor for yieldably biasing an intermediate element ofsaid gearing in one direction with a substantially constant torque notonly to maintain a constant tension on said line but also to take upbacklash in said gearing.

8. A measuring device comprising, in combination,- a rotatable take-upreel, a flexible line wound about said reel and arranged with one endanchored thereto and the other arranged to be unreeled from it, arevolution counter calibrated in terms or units of measure and includinga rotatable driving member, means for manually resetting said revolutioncounter, means for connecting said driving member and said reelincluding a friction clutch having frictionally engageable driving anddriven elements, and means including a brake for holding the drivingelementof said clutch against movement during actuation of said manualreset means to prevent variations in line tension during the resettingoperation.

9. In a device of the type set forth, the combination with a take-upreel having a flexible line thereon and arranged to be unreeled from it,of a housing .enclosing'the extended portion of the line, said housinghaving one side closed by a flap of yieldable material, and a membermovable along said housing and connected to said line within saidhousing, said member extending through said housing along the free endof said flap.

10. In a measuring apparatus, the combination of an indicatormechanisms. rotatable drum connected in driving relation with saidindicator mechanism, means defining a helical groove on the drumperiphermfa flexible line wound about said drum in said groove with oneend anchored to the drum and the other led freely from the drum andattached to a movable member whose position is to be indicated, the

portion of said member to 'which'the line is attached being movablealong a predetermined path, means for biasing the drum to reel in theline, and means supporting said drum in position to maintain theunreeled line adjacent the drum at substantially the true helix angle ofsaid groove relative to said path in all positions of said member alongsaid predetermined path.

' 11. Apparatus for measuring the displacement of a member movable alonga rectilinear path having, in combination. an indicator, a rotatabledrum having a driving connection-with said indicator and held againstaxial movement, a

flexible line helically wound around said drum ata constant helix anglewith one end led from the drum and fastened to said member, and

means supporting said'drum in a position to maintain a constant anglebetween the unreeled portion of the line and said path incall positionsof said member.

12. For use in a device of the type described, a tape take-up reelcomprising a rotatable drum having a. precision formed peripheralsurface which is a surface of revolution about the axis of rotation ofsaid drum, said drum surface hav-v ing a helical groove of constant leadtherein, and a member encircling said drum and fitting in said groove todefine between its convolutions a helical channel with an accuratelyformed root on the drum periphery.

13. A measuring device comprising, in combination,- a revoluble member,means for revolving leasably holding said driving element of theconnecting means against rotation due to drag exerted thereon byrotation of the driven element incident to resetting of the counter.

14. A measuring device comprising, in combination, a revoluble member,means for revolving said member through an angular distance proportionalto the displacement of a second movable member whose position is to beindicated, a revolution counter including a rotatable driving member,means for connecting said driving member in driven relation with saidrevoluble member but permitting independent rotation of said drivingmember relative to the revoluble member when the latter is positivelyheld against rotation, means for resetting said counter, and means forreleasably holding said revoluble member against rotation during theoperation of said resetting means.

15. Measuring apparatus comprising, in combination, a rotatable drum, aflexible line having a portion helically wound in a single layer and ata constant helix angle around said drum for rotation therewith, theremainder of said line being unreeled, means providing an elongatedguideway, a member movable along said guideway and guided thereby, asecond member stationary relative to said guideway, means connecting apoint on said unreeled portion to one of said members, means rotatablysupporting saidv to rotate said drum and to reel in said line, and

means controlled by the rotation of said drum during winding andunwinding of said line for indicating the extent of movement of saidmovable member.

16. Apparatus for measuring the relative move. ment between two membersalong a predetermined path comprising, in combinatioma drum rotatablymounted on one of said members, a flexible line wound helically aroundthe drum with a point on the unreeled portion of the line connected tosaid other member whereby said line is wound onto and unwound from thedrum dur-' ing relative movement between said members in oppositedirections, means acting during such relative movement to maintain thedrum axis and the unreeled portion of said line adjacent said drum ata-constant angle deviating from a right angle by an angle equal to thehelix angle of the wound line, and means tending to rotate said drum andreel in said line while maintaining the latter taut.

17. Measuring apparatus having, in combination, a movable supportingmember, means guidl supporting said drum on the other of said memberswith the drum axis extending transversely of said plane and with thepoint of lead-oil of the line from said drum spaced from the plane andmoving progressively away from the plane to maintain a constant anglebetween the plane and the unreeled portion of the line during unwindingof the line by relative movement between said members, and means tendingto wind up said line on the drum and maintain the line taut.

1B. A device of the type described comprising, in combination, arotatable drum, indicator means connected in driven relation with saiddrum, a flexible line wound helically about said drum and arranged withone and anchored to the.

drum and the other led freely from it to revolve the drum as the freeend of said line is reeled in or out, means supporting said drumforpivotal movement about an axis normal to its axis of rotation andpassing through a point of tangency between the drum periphery andthelast convolution of the line when the line is reeled in, and meansfor adjusting'the position of said drum about said pivotal axis todistribute the effect of any variations in drum diameter orline'thickness throughout the range of registration of the de'-' vice.

19. A device of the type described comprising, in combination, a sleevehaving a shaft journaled centrally therein, a casing at one end of saidsleeve having an indicating device therein connected in driven relationwith said shaft, a drum revolubly mounted at the other end of saidsleeve coaxial with said shaft and connected in driving relation withthe same, a flexible line wound helically about said drum and arrangedwith one end anchored to the drum and the other led freely from the drumto revolve the same as the free end of the line is reeled in or out, andmeans supporting the assembly set forth for pivotal movement about anaxis normal to, the axis of drum rotation and passing through the pointof tangency between the drum and the last convolution of said line.

20. In a device of the type described, the combination of v a revolubletake-up reel having a flexible line helically wound about the same withone end anchored to the reel and the other free to be unwound from itand thereby revolve the reel, the portion of'the line leaving the reelhaving an endwise motion in a direction substantially normal to therotational axis of the reel, indicator means responsive to angularrotation of the reel, and means by which the reel may be tions in reeldiameter.

21. In a device of the type described, the combination of a revolubletake-up reel having" a flexible line helically wound about the same withone end anchored to the reel and the other free to be lmwound from itand thereby revolve the reel, the portion of the line leaving the reelhaving an endwise motion in a direction substantially normal to therotational axis of the reel, indicator means responsive to angularrotation of the reel, and means supporting said reel for tiltingadjustment longitudinally of the path of travel of the portion of theline leaving the reel.

22. Measuring apparatus having, in combination, a rotatable drum, aflexible line having an unreeled portion and a portion helically woundon said drum in a single layer, means tending to rotate said drum and toreel in said line while maintaining the latter taut, means controlled bythe rotation of said drum during winding and unwinding of the line forindicating the extent of rotation of the drum in units of measure, twosupports guided for movement relative to the other along a rectilinearpath, means on one of said supports connected to the unreeledportion ofsaid line at a point spaced from the drum, and means .on the other ofsaid supports rotatably supporting said drum with the unreeled portionof the line intersecting said path at a constant angle in all positionsof the movable support and with the drum axis inclined relative to aperpendicular to said path in a direction and by an amount sufllcient tocompensate for cumulative dimensional inaccuracies in the drum and lineand cause said indicating means to register the correct displacement ofsaid movable support at spaced positions-in its range of movement.

23. Measuring apparatus having, in combination, a rotatable drum,.aflexible line helically wound on said drum, means tending to rotate saiddrum and to reel in said line while maintaining the latter taut, meanscontrolled by the the. movable member along said path to be changedprogressively by an increment suiflcient to cause said indicating meansto register cor'-' rectly the displacement of said movable member inspite. of the oversize or undersize ofthe drum.

24. Measuring apparatus having, in combination, a rotatable drum, 2.flexible line helically wound on said drum, means tending to rotate saiddrum and to reel in said line while maintaining the latter taut, twosupports guided for movement relative to each other along apredetermined plane, means connecting one of said supports to the freeend of the unreeled line, and means rotatably supporting said drum withits rotational axis. extending transversely of said plane'but tiltedaway from a perpendicular thereto whereby the amount of line paid outper unit of movement of the movable support changes progressively as theline cross-travels along the drum; 25. Measuring apparatus having, incombination, a rotatable drum, a flexible line helically wound on saiddrum, means tending to rotate said drum and toreel in said line whilemaintaining the latter taut, two supports guided for movement relativeto each other along a predetermined plane, one support being connectedto the free end 01- the unreeled portion or the line and the othersupport rotatably supporting said 26. Apparatus of the characterdescribed comprising, in combination, a rotary drum, a linewoundthereon-at a constant helix angle, means for eflectingrelativemovement between the free end of said line and the drum axis.along afixed path to maintain a constant angle equal'to said helix anglebetween said path and the unwound portion of said line adjacent to saiddrum, and means for mounting said drum with its axis inclined from aperpendicular to said path at such an angle that the amount of said linepaid out on unreeling thereof per unit of said relative movement will beincreased or decreased by an amount which compensates for the oversizeor undersize of the diameter of said drum.

27. Apparatus of the character described comprising, in combination, arotary drum, a line. wound thereon at a constant helix angle, means foreffecting relative movement between the free end of said line and thedrum axis along a fixed path to maintain a constant angle equal to saidhelix angle between said path and the unwound portion of said lineadjacent to said drum, and means for uniformly varying the'amount ofsaid line paid out or reeled in per unit of said relative of saidindicator element per unit of movement of said movable member along saidpath to be changed progressively by an increment suflicient tocompensate for inaccuracy in the size of said drum and thereby cause theelement to register correctly the displacement of said her.

29. Measuring apparatus having, in combinamovable memtion, a rotatabledrum, a flexible line helically indicator element to be changedprogressively in wound on said drum, two members mounted for movementrelative to each other along a predetermined path, one member beingconnected to the unreeled portion oi said line and the other memberrotatably supportingsaid drum, an indicator having a movable element forregistering the relative movement between said members,-

said line to cause the ratioof transmission of the motion between saidmovable member and said a sense and at a rate suflicien-t to compensatefor inaccuracy in the size ot'said drum whereby said indicator registersthe correct displacement of said movable member in all positions of thelatter along said path.

30. Measuring apparatus having, in combina tion, a rotatable drum, aflexible line helically the unreeled portion of said line and the othermember rotatably supporting saiddrum, an indicator having a movableelement for registering the relative movement between said members, and

means for driving said indicator element in accordance with the rotationof said drum; said driving means, said drum, and said line forming 10 amotion-transmitting connection between said indicator elementand-sa-idmovable element'having a driving ratio which, duringdisplacement ot said movable member, changes progressively in a senseand at a rate su'flicient to compensate i'or inaccuracy in the size ofsaid drum whereby said" indicator registers the correct displacement ofsaid movable member in all positions of the latter along said with. I

' ERIC 8. GU'I'I'MANN.

